Also, these bans aren't very common in professional level play, so why are these champions so often banned at the 1100-1400 ELO? Please note I'm talking about a specific ELO so the answer would be different than the link above.

Most of the banned champions here are incredibly disruptive in team-fights. Players at this level might not know when to fight, when to back out, or how to position themselves properly.
–
DanteDec 24 '12 at 22:07

3 Answers
3

1100-1400 ELO is a point where players aren't too familiar with the more difficult concepts of the game yet.

If Amumu isn't banned, who is going to kill him? In a coordinated and balanced teamfight, it's highly unlikely anyone but the ranged AD is able to effectively stop him. (Tanks are usually banned because they are harder to kill.) Many players may not know how to position themselves, or to stay alive so these hard to kill champions may be considered overpowered at this ELO.

Who wants to chase Singed through a mile of poison gas? Who wants to be hit into the air by a scary piece of rock? A lack of competency is most likely present at this ELO so therefore certain champions are able to take advantage of this and contribute more to the team.

At professional levels, more strategy definitely occurs during champion selection, but at this specific ELO which most of LoL's ranked players are in, these bans occur often due to the reasons above.

The higher elo players ban champions for particular reasons in mind. These eventually traverse down to lower elo games where everyone is seeing these champions banned and perhaps do not even know why.

Blitzcrank is banned frequently because of his Q, E, R combo. Yet if blitz crank misses his Q he is quite useless until it comes up and this is especially evident when he is supporting bot lane in the early game. When blitz miss his Q, the other team then can harass and shut down the other side completely until it is back up.

However, these are referred to as "overpowered" or "cheap" champions because they can catch a player off guard and simply put, wreck them.

Another reason all the same champs are banned is because, people will complain and blame losing the game on you. (If you are losing, of course)